This study was initiated to understand the merozoite and erythrocyte factors in the eventual interiorization of the merozoite within the erythrocyte. The research at present is to determine: (1) the receptor system on erythrocytes for initiating invasion of Plasmodium knowlesi, P. vivax and P. falciparum; (2) the role of erythrocyte metabolism in parasite invasion and development; and (3) the merozoite structure in the surface coat that attaches to the receptors. BIBLIOGRAPHIC REFERENCES: Miller, L.H., Powers, K.G., and Shiroishi, T.: Protective immunity and antimerozoite antibodies. Exper. Parasitol. 41: 105-111, 1977. Aikawa, M., and Miller, L.H.: Ultrastructural changes in the erythrocyte plasma membrane in oval-type malarial parasites. J. Parasitol. 63: 152-154, 1977.